This invention relates to lubricant compositions containing small amounts of sulfurized oleic alkyl esters or sulfurized alkyl esters of oleic acid-containing vegetable oils as load-bearing additives. It further relates to methods of preparing the additives.
There are generally two types of load-bearing lubricant additives, "antiwear" and "extreme pressure" (EP). When two lubricated surfaces are pressing against each other under a light load, they are separated from each other by a film of oil. As the load increases the film becomes thinner, and an antiwear additive is added to the lubricant to strengthen the film. However, under extreme pressure conditions the film strengthening properties of the antiwear additives become ineffective and the oil film collapses and the metal surfaces weld. EP additives contain components which prevent welding by reacting with the metal surfaces to form a coating of inorganic metal compounds.
Sulfurized sperm oil has long been recognized as an efficient EP additive for many lubrication oils. However, due to the fact that sperm whales are on the endangered species list, there has been much activity in the search for replacements for this desirable product. Sulfurized fatty oil and esters such as the synthetic esters of oleyl oleate and sulfurized lard oil are some of the compositions having EP properties which are similar to sulfurized sperm oil.
We have found a method for preparing sulfurized compounds suitable for use as extreme pressure lubricant additives from oleic alkyl esters and oleic acid-containing vegetable oils which comprises reacting one part of an oleic acid-containing vegetable oil dissolved in about 13 parts toluene or other suitable solvent which a stoichiometric excess of hydrogen sulfide at about -20.degree. C. in the presence of a catalytic amount of boron trifluoride.